Rendering/cropping

Hi all, I have footage shot at 2.7k and also 4k, both at 30fps. From what I remember, I can crop the 4k footage to 2.7 settings to help "stabilize"/"zoom" in. If I don't, the 4k footage will look better than the 2.7 footage when rendered since it has better resolution. Is that correct?

Also, I plan on uploading to Vimeo and YouTube. If I choose to render to 2.7k, will YouTube compress it and upload it to the 2k format or 2.7k?

Given what I want to do, what's the best render settings for 2.7k? Thanks!